This invention relates in general to laser imaging systems and more particularly to thermographic laser imagers having improved image quality.
Thermally processed media are widely used in a variety of applications, such as in medical, industrial and graphic imaging fields. For example, medical laser imagers reproduce diagnostic images on thermally processed photothermographic film. After the thermal film is exposed it, it developed by means of a heated member, such as a rotatable heated drum. Subsequently, the film (media) is cooled and output to a user.
U.S. Pat. No. 6,007,971, issued Dec. 28, 1999, inventors Star et al., discloses a commercially successful apparatus, system and method for processing photothermographic elements. After exposure to a diagnostic/medical image, the exposed photothermographic film is thermally developed by bringing the film into contact with a rotating heated drum having a resilient layer, with a plurality of rollers holding the film to the drum.
The rollers are mounted in brackets which can be lifted away from the heated drum to allow easier access to the drum for cleaning, and for clearing any jams that may occur of film being transported through the thermal processor.
During thermal development the exposed film is sensitive to roller pressure variation. Any roller skew out of roundness may cause an image artifact of cross web banding. This cross web banding is typically due to pressure variation as the film is transported through the pressure roller and drum. This image artifact may repeat itself down web and its frequency typically corresponds to the roller circumference. The non-uniform pressure between the pressure rollers and drum also increases optical density variations of the film. The entrance and exit of the film is a key parameter with respect to image artifacts due to non-uniform pressure. Velocity variation as the film exits or enters the drum may result in lifting the rollers or increase contact with the heated drum. These pressure and contact changes also result in an increased optical density variation of the film. There is thus a need for a thermal processor with improved image quality.
According to the present invention, there is provided a solution to these problems.
According to a feature of the present invention, there is provided a thermal processor for heat processing exposed thermographic media comprising: a heated drum for heating thermographic media brought into contact with the said drum; a centrally located assembly for supporting said drum for rotation; a plurality of spaced rollers located around a segment of said drum for holding media into contact with said drum; and a plate assembly for mounting said plurality of rollers for movement between a first position in contact with said drum and a second position out of contact with said drum, said plate assembly having first and second spaced alignment plates having circular features that align with a bearing assembly when said plate assembly is in said first position, whereby said rollers are aligned with said drum.
The invention has the following advantages.
1. Self aligning pressure roller assembly that accounts for process and manufacturing variability.
2. Removable cover for serviceability and system cleaning.
3. Improved optical density performance due to uniform pressure between rollers and drum.